The impact of aluminium stress on activities of enzymes of the oxidative metabolism: superoxide dismutase (SOD), ascorbate peroxidase (APX), peroxidase (POD), NADH peroxidase (NADH-POD) and oxalate oxidase (OXO) was studied in barley (Hordeum vulgare L. cv. Alfor) root tips. SOD appeared to be involved in detoxification mechanisms at highly toxic Al doses and after long Al exposure. POD and APX, H2O2 consuming enzymes, were activated following similar patterns of expression and exhibiting significant correlation between their elevated activities and root growth inhibition. The signalling role of NADH-POD in oxidative stress seems to be more probable than that of OXO, which might be involved in Al toxicity mechanism.